Hello @Nader ibrahimi
The two lists you provided represent different ways of categorizing STP types. Both are technically correct, but they emphasize different aspects of STP versions and implementations.
To clarify, the six-type list is more comprehensive and includes both standard IEEE protocols and Cisco-proprietary enhancements, while the four-type list consolidates them into broader categories...
The six-type list provides a detailed breakdown of STP variations. It includes:
- STP (Standard Spanning Tree Protocol): This is the original IEEE 802.1D protocol designed to prevent Layer 2 loops in networks. It operates with a single instance for the entire network and has slower convergence times of about 30-50 seconds.
- RSTP (Rapid Spanning Tree Protocol): An IEEE 802.1w standard, RSTP improves convergence significantly by introducing faster state transitions and new port roles, making networks more efficient.
- PVST (Per VLAN Spanning Tree): A Cisco-proprietary protocol based on STP, PVST creates a separate STP instance for each VLAN. This allows VLAN-specific load balancing and redundancy but uses more CPU and memory resources on switches.
- Rapid PVST (Per VLAN Rapid Spanning Tree): Cisco’s enhancement of RSTP, which offers faster convergence while maintaining per-VLAN instances for more granular control.
- MSTP (Multiple Spanning Tree Protocol): Defined in IEEE 802.1s, MSTP allows grouping multiple VLANs into a single STP instance. This reduces resource consumption and improves scalability in larger networks.
- MST (Cisco’s implementation of MSTP): While often used interchangeably with MSTP, MST can refer specifically to Cisco's implementation with additional optimizations and compatibility features for Cisco devices.
The four-type list simplifies the classification by consolidating these types into broader categories:
- CST (Common Spanning Tree): Refers to the original IEEE 802.1D STP, which operates with a single spanning tree instance for all VLANs.
- PVST (Per VLAN Spanning Tree): Cisco’s proprietary STP implementation with per-VLAN instances.
- RPVST (Rapid PVST): Cisco’s version of RSTP that combines rapid convergence with per-VLAN control.
- MSTP (Multiple Spanning Tree Protocol): The IEEE standard for mapping multiple VLANs into fewer STP instances, improving efficiency and scalability.
The main differences between these STP types lie in their speed, scalability, and resource consumption. STP (CST) is the slowest, with convergence times of 30-50 seconds, while RSTP and its derivatives (Rapid PVST) offer much faster convergence, typically within a few seconds. The VLAN management approach also varies: CST and RSTP use a single instance for all VLANs, while PVST and Rapid PVST create separate instances per VLAN for finer control at the cost of higher resource usage. MSTP strikes a balance by grouping multiple VLANs into fewer STP instances, making it more efficient for larger networks.
Best regards
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